Semiconductor pressure sensor including multiple silicon substrates bonded together and method of producing the same

Abstract

A small, precise semiconductor pressure sensor has a flat, thin diaphragm of uniform thickness that is formed by a simple process. A first silicon substrate and a second silicon substrate are bonded to each other with an interface insulating film interposed between them and circuitry including gauge resistors is fabricated on the primary surface of the second silicon substrate. The interface insulating film may be disposed in the recess of a vacuum chamber and may have a two layer structure. If alignment marks are formed, the circuitry can be accurately formed relative to the vacuum chamber.

What is claimed is: 
     
       1. A semiconductor pressure sensor comprising: a first silicon substrate having a primary surface and including a recess serving as a vacuum chamber;   a second silicon substrate having a primary surface, circuitry disposed on said primary surface of said second silicon substrate comprising diffused resistors and diffused wiring, and a secondary surface bonded to said primary surface of said first silicon substrate;   an interface insulating film interposed between said primary surface of said first silicon substrate and said secondary surface of said second silicon substrate; and   a silicon oxide film disposed on said primary surface of said second silicon substrate to protect said device.   
     
     
       2. The sensor according to claim 1 wherein said interface insulating film includes two layers. 
     
     
       3. The sensor according to claim 1 wherein said interface insulating film is disposed on said first silicon substrate in the recess. 
     
     
       4. The sensor according to claim 1 comprising silicon oxide films disposed on at least one of said primary and secondary surfaces of said second silicon substrate. 
     
     
       5. The sensor according to claim 1 comprising a glass coating disposed on substantially all of said primary surface of said second silicon substrate. 
     
     
       6. The sensor according to claim 1 comprising a glass coating disposed on substantially all of said primary surface of said second silicon substrate except on a part opposite the vacuum chamber. 
     
     
       7. A semiconductor pressure sensor comprising: a first silicon substrate having a primary surface;   a second silicon substrate having a primary surface, circuitry disposed on said primary surface of said second silicon substrate comprising diffused resistors and diffused wiring, and a secondary surface bonded to said primary surface of said first silicon substrate;   an interface insulating film interposed between said primary surface of said first silicon substrate and said secondary surface of said second silicon substrate, said interface insulating film defining a vacuum chamber between said first and second silicon substrates and forming alignment marks;   alignment mark observation windows disposed at positions of said second silicon substrate corresponding to respective alignment marks; and   a silicon oxide film disposed on said primary surface of said second silicon substrate to protect said circuitry and said alignment mark observation windows.   
     
     
       8. The sensor according to claim 7 wherein said interface insulating film includes two layers. 
     
     
       9. The sensor according to claim 8 wherein a part of one of said two layers of said interface insulating film is missing, thereby defining said vacuum chamber. 
     
     
       10. The sensor according to claim 1 comprising a glass coating disposed on substantially all of said primary surface of said second silicon substrate. 
     
     
       11. The sensor according to claim 7 comprising a glass coating disposed on substantially all of said primary surface of said second silicon substrate except on a part of that primary surface opposite the vacuum chamber. 
     
     
       12. A method of producing a semiconductor pressure sensor comprising: forming a recess in a part of a primary surface of a first silicon substrate as part of a vacuum chamber;   bonding part of said primary surface of said first silicon substrate to a primary surface of a second silicon substrate with an interface insulating film interposed between said primary surfaces with the recess at a central part of said surfaces;   machining a second surface, opposite said primary surface, of said second silicon substrate until the thickness of said second silicon substrate is reduced to a predetermined diaphragm thickness;   forming openings through certain portions of said second silicon substrate adjacent the recess, thereby exposing certain portions of said interface insulating film;   etching the exposed portions of said interface insulating film, thereby providing access to the recess;   closing the openings by depositing a film in the openings in a reduced-pressure ambient, thereby transforming the recess into a vacuum chamber;   forming a silicon oxide film on a primary surface of said second silicon substrate which has been formed by machining; and   fabricating, on said primary surface of said second silicon substrate, circuitry including diffused resistors and diffused wiring using said silicon oxide film as a mask, said silicon oxide film thereafter serving as a protective film.   
     
     
       13. A method of producing a semiconductor pressure sensor comprising: forming alignment mark observation holes on a first surface of a second silicon substrate;   forming, on a primary surface of a first silicon substrate, a recess which is to constitute a vacuum chamber;   forming, on said primary surface of said first silicon substrate, alignment marks having predetermined positions relative to said recess;   bonding said primary surface of said first silicon substrate to said first surface of a second silicon substrate in a reduced-pressure ambient with an interface insulating film interposed between said bonded primary and first surfaces, the bonding causing said recess to be transformed into a vacuum chamber;   machining said second silicon substrate at a second surface opposite said first surface to open alignment mark observation windows through which said alignment marks can be observed and to reduce the thickness of said second silicon substrate to a predetermined diaphragm thickness; and   fabricating, on said second surface of said second silicon substrate which has been formed by said machining, circuitry including diffused resistors, diffused wiring, metal electrodes, and a surface protective film, said circuitry being disposed opposite the vacuum chamber.   
     
     
       14. A method according to claim 13 comprising forming said recess by removing a part of said interface insulating film.